Using fabrics as strain and/or pressure sensors is desirable in many applications such as furniture, apparel, composites for vehicles, landscape, dams and highways as well as buildings. Advantages of fabric sensors are flexible, cost effective and ease in manufacturing and handling.
Textiles, whose electrical resistance changes under deformation, have been described previously. In U.S. Pat. No. 4,715,235, the change of the resistance of knitted or woven fabrics is mainly caused by the change of the ratio of the insulating portion to the conducting portion of the fibers at the intertwined regions in the fabric. This system involves two portions, i.e., insulating and conductive portions in the fabric, which increases the complexity of the fabric system and more important, and the instablization of the resistance-strain relationship during dynamic deformation which limits the application fields due to intrinsic properties difference between the two portions. In U.S. publication no. 20030119391, the inventors disclose a conductive pressure sensitive textile that is constructed by two orthogonally contacted filaments. The fabric can be used as a flexible switch to detect contacts on the fabric sheet. However, this system cannot measure the magnitude of the applied force accurately due to the filament yarn structure. In U.S. publication no. 20040252007, flexible switching devices are described comprising two self-supporting textile electrodes sandwiching a variably resistive element. In U.S. Pat. No. 4,659,873, fabric touch sensors are manufactured by two conductive fabric layers. These above two prior art documents (including other patents about capacitive touch sensors) commonly employ two or more layers to accomplish the detecting functions. Such arrangements increase the thickness, weight, and cost of the sensors with some other disadvantages such as low accuracy, instability, etc.